With the development of information communication technology, various wireless communication technologies have been developed. Among them, a WLAN is a technology that enables wirelessly accessing the Internet in households, enterprises, or a specific service providing area by using portable terminals such as a personal digital assistant (PDA), a laptop computer, a portable multimedia player (PMP), a smart phone, a tablet PC, and the like based on wireless frequency technology.
A standard for the WLAN technology has been developed as the Institute of Electrical and Electronics Engineers (IEEE) 802.11 standard. IEEE 802.11a provides a transmission speed of 54 Mbps by using an unlicensed band at 5 GHz. IEEE 802.11b provides a transmission speed of 11 Mbps by applying a direct sequence spread spectrum (DSSS) at 2.4 GHz. IEEE 802.11g provides a transmission speed of 54 Mbps by applying orthogonal frequency division multiplexing (OFDM) at 2.4 GHz. IEEE 802.11n provides a transmission speed of 300 Mbps to four spatial streams by applying multiple input multiple output-OFDM (MIMO-01-DM). The IEEE 802.11n supports a channel bandwidth of up to 40 MHz and in this case, provides a transmission speed of 600 Mbps.
As the supply of the wireless LAN is activated and applications using the wireless LAN are diversified, the need for a new wireless LAN technology for supporting a higher throughput than a data processing speed supported by the IEEE 802.11n has increased. A very high throughput (VHT) wireless LAN technology is one of the IEEE 802.11 wireless LAN technologies proposed in order to support a data processing speed of 1 Gbps or higher. Among them, IEEE 802.11ac is a standard for providing a very high throughput in a band of 6 GHz or less and IEEE 802.11ad is a standard for providing the very high throughput in a 60 GHz band.
Besides, a standard for various wireless LAN technologies is stipulated and the standard is being developed. Representatively, IEEE 802.11af is a standard for operating the wireless LAN in a TV idle band (white space), IEEE 802.11ah is a standard for supporting many terminals that operate at low power, and IEEE 802.11ai is a standard for fast initial link setup (FILS) in a wireless LAN system. In recent years, in a dense environment in which multiple base stations and terminals are present, development of an IEEE 802.11ax standard for improving frequency efficiency is in progress.
Due to an explosive increase of wireless LAN networks having various standards, interference among wireless LAN apparatuses which access different adjacent access points (APs), that is, belong to different basic service sets (BSSs) increases day by day and particularly, in WLAN 802.11ac, as a channel width of 20 MHz/40 MHz/80 MHz/160 MHz and a band of 5 GHz are used which are a wider channel width and a wider frequency band than the 802.11n using bands of 2.4 GHz and 5 GHz and a channel width of 20 MHz/40 MHz, a possibility that channels partially overlapped or completely overlapped between neighboring access points (APs) will be used further increases and the resulting interference problem comes to the fore as an important issue to be solved. Therefore, a scheme for efficient discovery considering a band and a channel width between adjacent APs using multi-bands is particularly required to efficiently use a frequency resource.
In order to minimize interference between the adjacent APs using the multi-bands and efficiently use the frequency resource, it is important for the AP to determine existence of the adjacent APs using the multi-bands which exist in an area to given interference thereto. In the discovery of the adjacent APs using the multi-bands, two following cases may be considered.
FIG. 1 illustrates a case in which AP1 and AP2 have a relationship of adjacent APs in which respective basic service set (BSS) coverage overlaps with each other, and as a result, using the same band and the same operating channel may interfere with both APs and in the BSS coverage of AP1 and AP2, both APs may detect mutual beacon signals. In this case, AP1 and AP2 do not have a hidden AP relationship with each other and a separate method for the adjacent AP discovery is not required. STA11 and STA12 are terminals that access AP1 and STA21, STA22, and STA23 are terminals that access AP2.
Meanwhile, in the case of FIG. 2, in which AP1 and AP2 have a relationship of adjacent APs which may interfere with each other when the respective BSS coverage overlaps with each other use the same operating channel and a partial overlapping operating channel in the same band, but both APs exist outside the respective BSS coverage in which both APs may not detect mutual beacon signals unlike FIG. 1. In this case, since AP1 and AP2 may not determine mutual existence for themselves, AP1 and AP2 have the hidden AP relationship and a method for discovering mutual existence is required to avoid interference between the BSSs of both APs, which occurs when the same and partially overlapped operating channels are used.